Organovo, a bioprinting company, has created small 4-millimeter discs of structured human liver tissue in a 3-D printing process. The discs can perform many of the same functions as a full-size liver, including testing how diseases progress.

The discs consist of about 20 layers of cells (harvested from spare tissue removed in operations) including the lining of blood vessels which help supply printed liver cells with oxygen and nutrients. This means the discs can “live” for over five days, and work in a similar way to real livers–this outperforms existing techniques which aren’t as versatile and only live for two days.

Ultimately the company hopes to print larger tissue masses which may be able to replace failing livers in real human patients–once it manages to print proper blood vessel structures into the tissue. 3-D printing of human tissue is a fast-growing field, and other success stories include human kidneys.